1. Field of the Invention
The present invention relates to a photoelectric switching device for a coordinate detection system and, more particularly, to such a photoelectric switching device for a coordinate data input device, a so called touch panel, to be installed in adjacent to an associated CRT (Cathode Ray Tube) display unit and the like.
2. Description of the Prior Art
Japanese Laid-open Patent No. 61,224/1987 discloses an arrangement such as that shown in FIG. 1, wherein 1 denotes a liquid crystal display unit, 2a, 2a denotes two mutually perpendicular linear arrays of infrared light-emitting elements or light emitting diodes for emitting infrared light along the lateral and longitudinal light paths, respectively, 3a, 3a denotes two mutually perpendicular linear arrays of associated photo-detector elements for detecting infrared light from respective light emitting diodes, and 4 denotes a user's finger placed on the face of display unit in such a manner as to block the infrared light along the lateral and longitudinal light paths A and B being emitted from the light-emitting diodes.
According to this system, each light emitting element 2a emits light one by one in a sequential manner under the control of control circuitry (not shown) and each associated photo-detector element 3a receives the light one by one in the same manner. If the light path A in the lateral direction and the light path B in the longitudinal direction are blocked respectively by a finger, for instance, the photo-detector elements 3a that correspond to the light paths A and B will produce a signal for indicating obstruction of the light paths. The control circuitry will then locate the spatial coordinates of the finger 4 by discriminating the sources of the signals produced by the photo-detector elements. Therefore, various operations such as change of display, control of optional equipment being installed, and the like are carried out by detecting the spatial coordinates of the finger 4 on a pattern (not shown) to be displayed on the face of display unit 1 for entering a switching input.
Such a prior art coordinate detection system has been installed in an instrument panel of an automobile for controlling a car audio system, an air conditioner and the like. In such a prior art system, the photo-detector elements arranged in the longitudinal direction along the light path B are normally installed at the upper portion of the display unit 1 for eliminating inadvertent operations to be caused by the ambient light such as the sun light. The detectors that conforms to the lateral direction along the light path A are installed at the left side of the display unit 1 for decreasing the influence of ambient light to a greater extent in the prior art system under such condition as the coordinate detection system is installed at the central part, between a driver's seat and the passenger seat, of the instrument panel. This is because ambient light from the driver's side is usually effectively blocked by a driver since the driver always occupies driver's seat at the right side in case of the right-hand steering-wheel vehicle however, it is hard to prevent ambient light from the passenger side from reaching the right side of the display unit 1 if no one is on the passenger seat.
Accordingly, in the prior art system, it has been difficult to avoid inadvertent operations merely by installing the photo-detecting elements at the left side of the display unit 1 even though ambient light from the driver's side is substantially blocked by the driver.
It is, therefore, a principal object of the present invention to eliminate the aforesaid difficulties and to provide a photoelectric switching device for coordinate detection systems having less susceptibility to inadvertent operations caused by ambient light.